Measuring weft feeders are normally used for feeding jet looms with weft yarn, the stopping element being used for limiting the weft yarn length and being removed from the passage slot for such a period of time that the exact weft yarn length is drawn off, the yarn circulating around the storage body in the course of this process. In the stopping position, the stopping element defines the circumferential stop for the circulating yarn. The stopped yarn extends from the last turn on the storage surface at an oblique angle to the stopping element and then approximately axially to a yarn guide element or a yarn-insertion or auxiliary nozzle exerting a pulling force on the yarn. At the end of the yarn-insertion movement, a whipping effect will occur when the yarn has struck the stopping element, said whipping effect causing a noticeable increase in the yarn tension and, subsequently, a relief of yarn tension, and this will exert an influence on the turns of yarn up to the last turns on the storage surface. The tension of the last turns of the yarn will be relieved to such an extent that these turns will hang down freely. This may result in a displacement of the turns and it may interfere with the next insertion. It may also happen that a loose last turn falls off the storage surface without any external influence so that the next weft yarn will then be too long. A turn falling down may wind itself around the stopping device and cause yarn breakage. Several superimposed turns may be registered as one turn during the next insertion, and this will result in malfunction. When the yarn geometry is changed between the measuring weft feeder and the edge of the woven fabric during the working cycle of the loom, very lively and highly twisted yarn qualities tend to slip away below the stopping element due to the pulling force exerted by the yarn-insertion or auxiliary nozzle, even if said stopping element engages a recess provided in the storage surface. This will result in incorrect weft yarn lengths and in yarn defects which will be visible in the woven fabric later on. In order to eliminate this disadvantage, the stopping element must move deeply into the recess with a long operating stroke and this necessitates an expensive and strong operating magnet having a delayed response behaviour.